Radio Frequency Identification (RFID) applications are proliferating as the economies of automated tracking and identification are being realized by the global community. RFID systems of tags and readers provide the ability to detect, read, and/or write data to tags that are affixed to “things” and/or persons to track and further to transfer this data to another computer-related or controlled device for either data storage or action. Cost and utility of the RFID tag are the predominant parameters dictating applicability of this technology.
Hospitals are particularly interested in investing in this technology. Location tracking utilizes a system comprised of tags that respond to a location stimulator, a trigger device (trigger) that cause a tag to respond and readers which record the tag's output signal that indicates presence and location.
There are two types of RFID tags in the marketplace: passive and active tags. Passive tags convert energy transmitted to them from a reader into a reflected signal that radiates back to the initiating reader device to effect communications. If a metallic or water-laden object is in front of the signal, then the tags will be blocked and not work. Passive readers are large and cumbersome and best suited to fixed installations as field tag read and write capabilities require large readers and direct line of sight. Active tags perform very well but are higher in cost than passive tags and therefore are restricted to specific applications that can carry a higher unit cost.
Battery powered (active RFID) tags provide more functionality, features and reliability than can be realized from passive tags. However, the cost of replacing drained batteries far exceeds the cost of the product and can be the criteria for selection of one device over another. For instance, a battery powered tag can be purchased for $10.00, but the cost of replacing the battery, primarily due to the labor costs of locating, disassembly and battery replacement can be $30-$120.00.
As a new class of RFIDs, active (battery powered) bimodal RFID tags suggest promise for a wide range of usages, particularly for indoor applications such as equipment inventory and location. Such tags include both RF and IR communication transmitters, receivers or transceivers, depending on their configuration. However, since they are active tags, they have not had significant impact on the field as they are limited in life by their battery capacity. Current batteries offered Lithium Thionyl Chloride for extended life; Lithium Magnesium coin-type cells for inexpensive, shorter lived applications; Lithium Iron Phosphate and Lithium Ion types (more expensive); and Alkaline.
For currently available active bimodal RFID tags having both RF and IR transceivers, the battery life is on the order of only ˜6-12 months for indoor use. This short battery life is due to the microprocessor instruction set algorithm awakening the tag from a partial power-down state to fully powered every 5 seconds for full processing of any signal detected. Typically, this process includes a scan of a few milliseconds (on the order of 1.5-2.5 msec) to detect an IR or RF signal. e.g., from an illuminator (also called a trigger device), and then an additional time period to fully process the signal for any identification information and signal message content to be acted-on. This frequent repeated cycling to full power to process all incoming signal information rapidly drains the battery, such that the battery must be replaced within ˜6-12 months to insure continued operation. In typical enterprises, such as hospitals, offices, manufacturing facilities, retail or warehouse operation, research facilities and the like, thousands of such tags are required to implement the equipment inventory and location systems. In addition to the cost of replacement batteries, the necessary staff, record keeping and logistic requirements to keep track of battery check and change-out has created a serious financial barrier to the adoption of such tags for such inventory/location systems.
Although there are improvements in battery technology, there is currently nothing on the horizon that promises more than an incremental 10-20% increase in battery life, not enough to change the financial adoption equation for systems employing active bimodal RFID tags.
In addition, in current systems, the illuminator is always on. However, that not only burns out the power supply of the illuminator, but also causes totally unacceptable “black-out” interference with all other equipment that uses IR or RF to communicate, such as televisions, CD players, computer mice and keyboards, radios, networks, and other IR controllers for equipment, including medical and industrial equipment.
Accordingly, there is a need in the art for a paradigm shift in tag system architecture and functional wake-up and scan algorithms by which such tags operate so that currently available batteries can be used in a manner that they have operational life spans of 5-10 times the currently expected battery life.